It's a really, really easy personal website CMS with support for all conceivable web services. With a huge focus on design. It allows everyone and their dog to set up a website - with flavors.me hosting it - and it's really hard to make an ugly webpage.
Companies, brands, celebrities, et a. can also use it to great effect.
Here are some example websites: http://flavors.me/community.
Someone compared it to FriendFeed, which I guess is fair, but I'd consider it more of a homepage than a social feed. It's a good way to find out where that person hangs out online - or to use as a portfolio/CV.